Electrostatic spraying is a process in which a liquid surface is charged by an applied voltage. When the electrical forces exceed the surface tension, the surface is disrupted to produce liquid jets or drops of liquid. Co-inventor Kim, with R.J. Turnbull, studied this phenomenon, as reported in 47 Journal of Applied Physics 1964-1969 (1976). That paper discussed the previous formation of single jets of liquids having high conductivity and the spraying at a slow rate of large drops of an insulator. The paper itself reported the spraying of a jet of FREON, an insulator, which broke up into drops, all larger than ten (10) microns in diameter.
Further research by co-inventor Kim with R. J. Turnbull and J.P. Woosley was reported in IEEE Transactions on Industry Applications, Vol. IA-18, No. 3 pp. 314-320 (1982) and 64 Journal of Applied Physics 4278-4284 (1988). These papers reported the electrostatic spraying of another insulator, liquid hydrogen. The smallest drops observed were larger than nine (9) microns in diameter.
None of the research described above produced nanodrops, or used the nanodrops to produce nanoparticles or either uniform or patterned thin film deposits.
It appears to the present inventors that this deficiency was the result of the fact that only a single charged jet was produced, which caused the drops resulting from jet breakup to be of a relatively large size compared to nanodrops.
U.S. Pat. No. 4,993,361 to Unvala on superficial examination might appear to be material to the present invention. However, Unvala merely atomizes and ionizes a liquid, then heats it to produce a vapor. The size of the drops which are produced is not disclosed.